Depending on the manner in which a medical container, such as an infusion solution bag, is used, liquid may remain in the container even after use. In cases where liquid remains in a medical container in this way, there are concerns that if a medical injection needle is removed from a stopper attached to the container, then liquid remaining in the container will leak out or spill. Therefore, stoppers for medical containers need to be resealable and have a liquid leakage-resistance.
Isoprene rubbers, butadiene rubbers, butyl rubbers and blends thereof are used for stoppers for medical containers from the perspectives of resealability and liquid leakage resistance. However, in cases where the rubbers mentioned above are used, it is necessary to carry out at least a step of adding an additive such as a filler, softener or vulcanizing agent and then kneading or a vulcanization step of supplying a kneaded rubber mixture to a mold for a stopper, and then heating and pressurizing. However, these steps are complex and require large-scale equipment, and therefore involve problems such as high production costs.
In addition, medical container stoppers of rubber mentioned above may cause a problem of degradation caused by double bonds in rubber components during storage, and degraded rubber components may transfer into liquid medicines.
Plastic needles replace conventional metal injection needles for reasons such as handlability and safety. Because plastic needles are less rigid than metal needles, the needle diameter must be greater in order to ensure needle rigidity. However, if the needle diameter increases, resistance (needlestick resistance) increases in piercing into a stopper for a medical container.
Stoppers made of thermoplastic elastomers have been proposed in recent years in order to solve the problems mentioned above. For example, Patent Document 1 discloses a stopper for medical use comprising a medical resin composition, which comprises a hydrogenated block copolymer, a hydrogenated petroleum resin, a poly phenylene ether resin, a peroxide decomposition type olefinic resin and a non-aromatic type rubber softener. In addition, Patent Document 2 discloses a rubber stopper for medical use, which is obtained by molding a resin composition that comprises a hydrogenated block copolymer, a softener for hydrocarbon-based rubbers, and a polyolefin-based resin.